In general, the basic steps for processing a light-sensitive material are a color developing step and a desilvering step. In the color developing step, exposed silver halide is reduced with a color developing agent to generate silver, and the oxidized color developing agent reacts with a coupler to form a dye image. In the following desilvering step, silver formed in the color developing step is oxidized by the action of an oxidizing agent (generally called a bleaching agent ) and the oxidized silver is then dissolved with an agent for forming a complex ion of a silver ion (generally called a fixing agent). After the desilvering step, the dye images thus formed (but no silver) remain on the light-sensitive material.
Usually, after these steps, washing (e.g., water washing) is carried out to remove .residual processing solutions entrained in the light-sensitive material.
In the case of a color paper and a reversal color paper, the processing is finished with the above steps and is generally followed by a drying step. In the processing of a color negative film and a reversal color film, an additional stabilizing step is necessarily provided between the fixing step and the drying step. It is well known that the stabilizing bath at the final step following the fixing and/or washing steps contains formaldehyde to prevent fading of the magenta dye image due to magenta coupler remaining in the light-sensitive material after processing. Some quantity of formaldehyde vapor is generated when the stabilizing bath containing formalin is prepared, and when the light-sensitive material containing stabilizing solution carried out from the processing bath is dried.
Particularly, the preparation of a stabilizing solution is the operation in which a condensate (usually called a kit) is diluted with water. There is a danger in the preparation of a stabilizing solution in contacting formaldehyde vapor of a relatively high concentration due to handling of the condensate having a high concentration of formalin.
It is known that the inhalation of formaldehyde vapor is harmful for humans, and the Japan Association of Industrial Health advises that an allowable concentration of formaldehyde in a working environment is 0.5 ppm or less. Therefore, efforts to reduce the concentration of formaldehyde in the stabilizing bath, and to replace formaldehyde with alternatives have been made to improve the working environment.
A hexamethylenetetramine compound is proposed, for example, in JP-A-63-244036 (the term "JP-A" as used herein means an unexamined published Japanese patent application) as an alternative for formalin. The use of this compound reduces the formaldehyde vapor pressure. However, the compound of JP-A-63-244036 restricts the anti-fading function of formaldehyde for a magenta dye, i.e., the reason for adding formaldehyde to the stabilizing solution, and causes a marked fading of the magenta image within several weeks even at room temperature.
Furthermore, use of N-methylol compounds such as urea, guanidine and melamine is proposed in the specifications of U.S. Pat. Nos. 4,786,583 and 4,859,574.
These compounds can clearly reduce the vapor pressure of formaldehyde, but the reduction in vapor pressure is not sufficient for practical use.
Furthermore, another aspect is that the incorporation of formaldehyde into a processing solution markedly deteriorates the stability of the processing solution. For example, the formaldehyde added to washing water and a stabilizing solution reacts with sulfite ion carried over from a fixing solution or bleach/fixing solution to thereby form a precipitate of sulfite in the processing solution.
The method for preventing such precipitate due to the presence of formaldehyde is described in U.S. Pat. No. 4,786,583, in which alkanolamine is used. However, this method although effective to some extent is not sufficient, and the above sulfurization takes place to cause turbidity and form a precipitate in the solution when the solution exchange rate is low.
Also in a bleaching solution and a conditioning solution (a bleach-accelerating solution) which is a prebath of the bleaching solution, the incorporation of formaldehyde likewise causes the deterioration of the processing solution. Furthermore, turbidity and the formation of a precipitate undesirably clog the filter of an automatic developing machine and the precipitate adheres to a light-sensitive material being processed.
Therefore, there is a need in the art for a technique which provides sufficient anti-fading function to a magenta dye image and reduces formaldehyde vapor pressure.